Fused crushed magnesia grain is normally used for insulating electrical resistance wires from an outer protective metal sheath. Various sources of magnesia are available for feed to the fusion process but currently a primary source of high quality ore for the production of electrical grade magnorite, requires shipment all the way from India. All commercial ores available heretofore have been relatively expensive and preparation of each of the respective ores for use has involved fusion, solidification, sorting, crushing, calcining and screening procedures that produce additional costs making the conventional electrical magnesia grain products relatively expensive as compared with the invention disclosed herein.
It is known that high temperatures are required to melt the purer magnesia ore used for electrical magnesia, i.e. those with a magnesia content in the order of 94 % or higher MgO and further that the molten product produced from such relatively pure sources of magnesia has a narrow solidification range that makes the tapping of the fusion bath difficult. For this reason fused magnesia used for electrical insulation purposes has heretofore been solidified in large masses requiring several stages of crushing to produce grains of a size to be used for electrical insulation and after crushing it has been found necessary to calcine the crushed product to make it useful as an insulation in the known electrical resistor type devices.